“Open” surgery is known to be very demanding for patients. For this reason, practitioners are increasingly using mini-invasive operations in which medical instruments are inserted into a natural duct of the patient (vagina, rectum, auditory meatus etc.) or into an artificial duct connected to the body of the patient (cannula, artificial vein, trocar etc.).
In urology, it is known that a prostate biopsy can be carried out to screen for possible prostate cancer. This involves taking tissue samples from within the prostate, said samples then being analyzed in a laboratory, to detect the presence of any cancer cells. For this, the patient lies on his side. An instrument comprising an ultrasound sensor and a needle guide with a biopsy needle is then inserted into the natural duct formed by the rectum. Using this instrument, the surgeon perforates the colon wall to access the prostate and thus take tissue samples.
To perform the biopsy the only images the surgeon can use are two-dimensional ones taken in real time by the ultrasound sensor. The surgeon therefore has to imagine a three-dimensional representation of the prostate in order to take the samples, in the knowledge that the prostate tends to be displaced or deformed by the movements of the instrument.
It therefore proves extremely difficult for a surgeon to know the exact locations from which the needle will take samples of prostate tissue. However, aspirations from the prostate should be done uniformly over the whole prostate, since cancer cells cannot be detected directly by the sensor.
Devices have recently been developed to help the surgeon perform the various types of aspiration very precisely. These new devices comprise sensors that can provide three-dimensional images of the prostate. The operating principle of said sensors is to plan the theoretical positions for the aspirations and to study the deformation of the prostate during the biopsy. The theoretical aspiration plan is then amended depending on the study of deformation of the prostate so that the aspirations can be done in the right places.
However, the sensors have to scan the prostate in order to provide three-dimensional images and thus produce images not in real time but with a few seconds' delay. Any movement of the sensor while it is scanning the prostate should therefore be limited as far as possible. Similarly, any unnecessary movement of the instrument when the biopsy needle is inserted into the prostate should be limited as far as possible, so that the aspiration can be done in the right place.
It is possible that the patient is not under local anesthesia and/or is not immobilized. This means that the patient—and thus all the tissues of the natural or artificial duct with which the instrument can come into contact—can move during the operation. Furthermore, it proves difficult for a surgeon to hold the instrument still in a given position to allow the sensor to scan the prostate and to carry out aspirations in the desired places.
To assist the surgeon, there are known devices for guiding an instrument comprising an articulated arm for moving a proximal end of the instrument. The surgeon can then control the articulated arm so that it locks the instrument in a given position. This makes it easy for the surgeon to perform an operation on the patient, such as taking a tissue sample or acquiring images via the sensor.
However, the instrument—locked in a given position like this—opposes any movements of the patient, which can be uncomfortable for the patient and even damage some tissues.
Thus there are known devices for guiding an instrument comprising an articulated arm for moving a proximal end of the instrument, the articulated arm being linked to the proximal end by a gimbal or ball-joint type link.
This means that, even if the surgeon controls the articulated arm so that it locks the instrument in a given position, the ball coupling or gimbal nevertheless allows the patient to move. But each time the patient moves, the instrument is then displaced and the surgeon has to reposition the instrument correctly.
Document WO 2011/058530 discloses a medical instrument guide comprising an articulated arm that can lock the medical instrument in a given position. The articulated arm is controlled so that when the effort exerted by the surgeon on the instrument exceeds a predetermined threshold of effort, locking of the articulated arm is released. However, the effort exerted is measured by effort sensors.